I made this recipe up tonight, and it was great.
Portobello mushroom caps
Mozzarella cheese (shredded)
Melt some butter in an oven ready pan (I used cast iron) and clean out the gills on the mushroom caps with a spoon. Place the caps in the pan on high, open side down.
Turn on your broiler and get that heated, as you'll be using it shortly. After the mushrooms start to sizzle, flip once to coat the tops with butter, then flip open side down again. Transfer the pan to the broiler for approximately 5 minutes or until the caps begin to get soft.
Remove the caps, flip over, and spoon tomato paste as you would a pizza crust. Sprinkle on italian seasoning, place pepperoni, cheese, (and more pepperoni!)
Return to the broiler until the cheese is starting to brown and gets bubbly.
SERVE!! This is definitely a knife and fork type of pizza, but if you're a mushroom fan it doesn't get much better.